Security fibers and process for the preparation thereof

ABSTRACT

Security fibers having enhanced antifalsification features are prepared by a process which comprises the steps of: i) braiding 5 to 30 denier fibers to form a twine; ii) dyeing the twine with a dye or pigment; iii) drying the dyed twine; and then iv) cutting the dried twine to give the security fibers in the form of cut fibers.

FIELD OF THE INVENTION

The present invention relates to security fibers, a process for thepreparation thereof and a security paper containing same.

BACKGROUND OF THE INVENTION

Security documents such as bank notes, stocks, bonds, checks, warrantsand identification cards need to be guarded by antifalsificationmeasures and they are often made from a security paper having a securityelement in the form of fibers, strips or threads embedded therein.

Japanese Laid-open Patent Application No. 90-293500 discloses a securitypaper containing security fibers prepared by dyeing a natural orsynthetic fiber uniformly with a visible or invisible fluorescent dyeand cutting the dyed fiber to a given length. However, suchmonochromatic security fibers have limited effectiveness in theprevention of counterfeiting.

Korean Patent No. 111,723 describes multi-colored security fibersprepared by a process comprising the steps of: placing a mask over asection of a fiber and dyeing the exposed section of the fiber with afirst dye; replacing the mask over to the dyed section thereby exposingthe undyed section; dyeing the undyed section of the fiber with a seconddye; and cutting the fiber to a suitable length to obtain multi-coloredsecurity fibers having an enhanced security feature.

However, this complicated process has a low productivity.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providean improved process for preparing security fibers suitable for use in asecurity paper.

It is another object of the present invention to provide novel securityfibers suitable for use in a security paper.

It is still another object of the present invention to provide asecurity paper containing security fibers having an enhanced securityfeatures.

In accordance with one aspect of the present invention, there isprovided a process for preparing security fibers which comprises thesteps of: i) braiding 5 to 30 denier fibers to form a twine; ii) dyeingthe twine with a dye or pigment; iii) drying the dyed twine; and iv)cutting the dried twine to give the security fibers in the form of cutfibers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the invention, whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of braided fibers in the form of atwo-thread twisted twine;

FIGS. 2 depicts a schematic diagram of braided fibers in the form of athree-thread twine;

FIG. 3 demonstrates one embodiment of the security fibers prepared inaccordance with the present invention; and

FIG. 4 illustrates one embodiment of the inventive security papercontaining embedded security fibers prepared in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In practicing the present invention, a 5 to 30 denier fiber 1, which maybe any one conventionally used in the art including natural fibers andsynthetic fibers such as polyamide, rayon, polyester and cotton thread,may be braided in the form of a two-thread twisted twine 21 as shown inFIG. 1, a three-thread twine 22 as illustrated in FIG. 2, a twinetwisted around a suitable pad, e.g., a wire, a twisted twine with amarking band and the like.

The braided fibers are dyed with a dye or pigment in a conventionalmanner. Exemplary dye or pigment which may be used in the presentinvention may be any one conventionally used in the art including aciddyes and direct dyes such as Acid Blue AS, Acid Rhodamine B, Uvitex,Papilion Yellow F, TBF(terasile brilliant flavine) and GFF.

The braided fibers dyed in accordance with the present invention havevarious shades of color because each fiber is partially masked by otherfiber(s) and sections thereof are dyed to different shades depending onthe degree of masking.

The shades of color in a fiber can be controlled by adjusting the extentof twist torsion and dyeing time. When the twist strength is high andthe dyeing time is short, the area of the twisted fiber which is tightlyshielded by other fibers may remain undyed as shown in FIG. 3 whereinthe portion 31 is dyed whereas the portion 32 is not dyed.

The dyed fiber may be cut by using any of the conventional method wellknown in the art to a given length, preferably 3 to 6 mm.

In practicing the present invention, the dyed and cut fiber may befurther dyed with another dye/pigment to obtain fibers having variousshades of two or more colors. The dye/pigment suitable for use in thesecond dyeing step may be any one conventionally used in the artincluding acid dyes and direct dyes such as Acid Blue AS, Acid RhodamineB, Uvitex, Papilion Yellow F, TBF(terasile brilliant flavine) and GFF.

When the second dyeing process is carried out at a high temperature,e.g., from 80 to 100° C., the fiber may be transformed into an S-shapedform, thereby enhancing its anti-counterfeiting feature.

The security fibers having varying color shades prepared in accordancewith the present invention may be used in manufacturing a security paperby employing any of the conventional papermaking method well known inthe art.

For example, the security fibers of the present invention may be mixedwith papermaking materials to provide a security paper containing thesecurity fibers uniformly dispersed therein as illustrated in FIG. 4.

The following Examples are intended to further illustrate the presentinvention without limiting its scope.

EXAMPLE 1 Preparation of Security Fiber

20 denier polyamide fiber was braided in the form of two-thread twine asshown in FIG. 1.

Acid Blue AS was dissolved in water at pH 4-5 to a concentration of 1-2wt % to obtain a dye solution. The braided fiber was added to the dyesolution and dyed at about 90° C. for 10-30 minutes, washed thoroughlywith warm water and dried. Then, the dyed fiber was cut to a length of3-5 mm.

The cut fibers above were dyed in a 1-2 wt % TBF solution at about 90°C. for 10-30 minutes, washed thoroughly with water and dried to givesecurity fibers of the present invention.

EXAMPLE 2 Preparation of Security Paper

10 wt % of a mixture of titanium dioxide, white carbon, talc and calciumcarbonate, and 0.1-1 wt % epoxy resin were added to a 0.2-1% wood pulpsuspension in stock chest to form a paper making stock.

The security fibers obtained in Example 1 were added to the paper makingcomposition obtained above, to a concentration of 0.002-1.0%. Themixture was stirred well and formed into a security paper of 60-100g/m².

While the invention has been described with respect to the abovespecific embodiments, it should be recognized that various modificationsand changes may be made to the invention by those skilled in the artwhich also fall within the scope of the invention as defined by theappended claims.

What is claimed is:
 1. A process for preparing security fibers havingvarying color shades which comprises the steps of: i) braiding 5 to 30denier fibers to form a twine; ii) dyeing the twine with a dye orpigment to form dyed portions and undyed portions on each fiber; iii)drying the dyed twine; and then iv) cutting the dried twine to give thesecurity fibers in the form of cut fibers.
 2. The process of claim 1,further comprising the step of v) dyeing the cut fibers with another dyeor pigment after step iv).
 3. The process of claim 1, wherein the twineis in the form of a two-threaded plait.
 4. The process of claim 1,wherein the twine is in the form of a three-threaded plait.
 5. Theprocess of claim 2, wherein the cut fibers are dyed at a temperatureranging from 80 to 100° C.
 6. A security fiber prepared by the processof any one of claims 1 to
 5. 7. A security paper containing the securityfiber prepared by the process of any one of claims 1 to 5.